Wireless communications devices such as the BlackBerry™ by Research in Motion Limited enable users to download map content from web-based data sources such as BlackBerry Maps™, Google Maps™ or Mapquest™. Downloaded map content is displayed on a small LCD display screen of the wireless communications device for viewing by the user. The user can pan up and down and side to side as well as zoom in or out. Due to the small display on the device and due to the limited over-the-air (OTA) bandwidth, there is a need to optimize the delivery and handling of the map data.
Constructing a map projection requires one to fit a curved surface onto a flat display which necessitates distorting the true layout of the Earth's surface. For example, an equirectangular projection, which is a cylindrical map projection, exaggerates the true characteristics of the Earth's surface close to the poles. In other words, the farther from the equator, the more that the equirectangular projection distorts the true size and proportion of features of the Earth's surface. Thus, for example, while east-west roads are not distorted, those with both a north-south and an east-west component appear slanted. Thus, in the northerly (or southerly) latitudes, roads that are in fact perpendicular appear to intersect at an angle.
With GPS-enabled or other “location-aware” wireless devices, if the map is rotated to show the direction of travel of the device, i.e. a “track up” orientation, then the path representing the current direction of travel path is rendered onscreen at a slight angle.
Although complex algorithms can be devised to compensate for this distortion phenomenon, the limited over-the-air (OTA) bandwidth and onboard processing capacity make these complex algorithms generally unsuitable for use on wireless communications devices. For example, Mercator projections require computationally intensive mathematics involving natural logarithms.
Accordingly, a technique for efficiently compensating for map projection distortions on wireless communications devices, particularly in the context of devices capable of showing the current direction of travel, remains highly desirable.
It will be noted that throughout the appended drawings, like features are identified by like reference numerals.